1. Field of the Invention
The present invention relates to a semiconductor optical amplifier device for performing induced emission by carriers in an active region and a method of using the same, such as an apparatus including the device and an optical communication system including the device.
2. Related Background Art
Conventionally, in prior art semiconductor optical amplifier apparatuses or devices, antireflection coatings are respectively formed on both opposite end surfaces of, for example, semiconductor laser structures, and population inversion is established in a high current injection state to amplify an input light by the induced emission.
However, since the amplification is conducted by injecting carriers into an active region of the prior art apparatus, the refractive index of the active region is varied in accordance with the injection state of carriers and a ripple wavelength caused by feedback at the end surfaces is changed.
When the injection current is small, the magnitude of ripple appearing in the amplification factor-wavelength dispersion characteristic is low and the change in oscillation wavelength will not largely affect the amplification factor in this wavelength range. In contrast thereto, when the injection current is large, the ripple of the amplification factor increases and the amplification factor is largely varied in response to only a small change in the amount of the injection current.